Alterations in dopaminergic neurotransmission in the basal ganglia are thought to play a major role in the pathogenesis of schizophrenia as well as of neurodegenerative disorders like Huntington's and Parkinson's disease. A detailed characterization of the mechanisms by which dopamine affects the activity of its target neurons is therefore of primary importance in the development of novel drugs, which could be useful in the treatment of these disorders. The long-term objective of this Research Project is the characterization of the role of protein phosphorylation in the intracellular signal transduction pathways of neostriatal dopaminoceptive medium spiny neurons. The Specific Aims of the project are centered on the study of the involvement of protein phosphatase-1 (PP1), and of its regulator DARPP-32 (a dopamine- and cAMP- regulated phosphoprotein-32kDa), in the control of various classes of effector proteins participating in the regulation of cell excitability, such as the electrogenic pump Na+,K+ATPase and voltage-dependent calcium and sodium channels. The regional and subcellular localization of PP1, Na+,K+-ATPase and calcium and sodium channels will be analyzed by means of light and electron microscopic techniques. The comparison of the distribution of these proteins in the neostriatum will provide the anatomical framework for a detailed analysis of the mechanisms modulating their state of phosphorylation and activity. Regulation of the state of phosphorylation of Na+,K+-ATPase and calcium and sodium channels will be evaluated both in vitro, using neostriatal slices and dissociated neurons, and in vivo, by means of pharmacological manipulation and selective brain lesions. The results of these studies will be followed by a careful examination of the effects induced by changes in the state of phosphorylation, on the activity of the various effector proteins. In these studies, cell biological and electrophysiological techniques combined with the use of genetically altered mice will be utilized to clarify the role of the DARPP-32/PP1 cascade in the intracellular signal transduction pathways of neostriatal dopaminoceptive neurons. The information obtained from all these approaches should extend our knowledge of the role played by dopamine and other neurotransmitters in the control of physiological responses of neostriatal neurons. Finally, the examination of the different phosphorylation systems under experimental perturbations will increase our understanding of the possible pathological changes taking place along the intracellular signalling pathways in neuropsychiatric disorders.